This invention concerns an assembly comprising a piston member which is axially slidable in a cylinder, a power assisted steering gear which includes such an assembly and a method of forming a piston member for use in such an assembly. More particularly the invention concerns a piston and cylinder assembly in which the piston member has a cylindrical piston part which is slidable axially and in sealed manner within the cylinder and has rod parts which project from axially opposite sides of the piston part, usually to extend in sliding and sealed manner from the opposed ends of the cylinder to provide convenient outputs from the assembly. Conventionally a piston member of the type aforementioned requires accurate machining in the manufacture of the rod parts and piston part and/or in the fitment of the rod parts to the piston part. Piston and cylinder devices find many uses in industry, especially where they may provide a single or double acting servo motor fluid pressure supply to which is controlled to assist in displacement of a component to which the assembly is coupled. This is particularly so in the automotive industry where a double acting piston and cylinder assembly is often utilised as a servo motor in a power assisted steering gear. In the automotive industry there is an ever increasing requirement for efficient, reliable and safe components and units which lend themselves to economic techniques of manufacture. It is believed that there is a need for a piston and cylinder assembly which is capable of satisfying these requirements and which has a piston member capable of being manufactured in a manner which alleviates expensive machining operations and to such accuracy and reliability that the piston and cylinder assembly may safely be incorporated in a power assisted steering gear. It is an object of the present invention to satisfy the aforementioned requirements.